Molecular evidence for sectional classification of shrub willows (Salix L. subg. Chamaetia/Vetrix) based on RAD sequencing data

下一代测序工具的兴起大大增加了研究人员分析非模型植物的机会。生物基因组学的发展使人们有可能重建生物的进化历史，并根据大量的测序数据评估现有的分类学概念。然而，大多数的方法和工具是用于二倍体属或明确定义的物种组在一个有限的地理区域。因此，处理频繁杂交、显示网状进化、多倍性和渐渗的分类学上困难的植物仍然具有挑战性。柳属（Salix L.）尤其是灌木柳树（subg. Chamaetia/Veetia）是北方半球的一组具有分类学挑战性的树木和灌木。该属植物雌雄异株，具有表型可塑性，杂交频率高，倍性范围从二倍体到二倍体不等。现有的分类修订是基于形态学和局限于当地地区。根据他们的说法，Chamaetia/Veelis包括约40个部分中的300多个物种。然而，柳属植物的整体分类还远未解决。尽管对柳属植物的研究已经进行了很长时间，但传统的种和组的分类从未用分子标记进行过检验。主要原因是传统标记系统缺乏信息字符。然而，新的测序技术，如RAD测序，产生成千上万的可变字符。本项目拟利用信息量大的RAD测序数据，对灌木柳树的断面分类和复杂演化进行分析，进行包括所有描述断面的全面取样。一个很好的解决包括几个物种的每节覆盖的分布范围将导致遗传框架，结合形态特征编码将有助于解开柳分类的挑战。根据分子数据，应进行多倍体的具体分析。最后，应建立hyRAD，这是一种允许将降解的DNA（例如来自植物标本材料）纳入RAD测序方法的方法。通过对一个定年演替过程的地理学分析，重建灌木柳树的时空演化。

The rise of next generation sequencing tools massively increases the opportunities of researchers to analyze non-model plants. The developments in phylogenomics make it possible to reconstruct the evolutionary history of organisms and to assess existing taxonomic concepts based on impressive amounts of sequenced data. However, most methods and tools are used for diploid genera or well-defined species groups in a restricted geographical region. Thus, dealing with taxonomically difficult plants that are frequently hybridizing, show reticulate evolution, polyploidy, and introgression is still challenging. The species-rich genus Salix L. and especially shrub willows (subg. Chamaetia/Vetrix) are such a taxonomically challenging group of trees and shrubs occurring in the Northern Hemisphere. The species are dioecious, show phenotypic plasticity, hybridize frequently and their ploidy level range from diploid to octoploid. Existing taxonomic revisions were based on morphology and restricted to local regions. According them, Chamaetia/Vetrix includes more than 300 species classified in about 40 sections. However, the overall taxonomy in Salix is far from resolved. Despite the long research in Salix, the traditional classification of species and sections has never been tested with molecular markers. The main reason was the lack of informative characters in traditional marker systems. However, new sequencing techniques as RAD sequencing produce ten thousands of variable characters. In the proposed project, the sectional classification and complex evolution of shrub willows shall be analyzed with the highly informative RAD sequencing data for a comprehensive sampling including all described sections. A well-resolved phylogeny including several species per section covering the distributional range will result in a genetic framework that combined with morphological character coding will help to disentangle the taxonomic challenges in Salix. Based on the molecular data, specific analyses on polyploidy shall be performed. Finally, hyRAD shall be established, a method that allows the inclusion of degraded DNA (e.g. from herbarium material) into a RAD sequencing approach. The spatio-temporal evolution of shrub willows will be reconstructed by biogeographical analyses of a dated phylogeny.